The main character has started a job as a lighthouse attendant, for an entire year, in a completely secluded location. At first he relishes the chance to be alone, but soon the complete isolation gets to him. I always take note of descriptions of isolation in stories, because that's one aspect of the Beast that always fascinates me. What is it like for him to be cut off from civilization, alone in a castle with unrealistic hopes as his only comfort? What does he do until Beauty comes?
Then the narrator decides to try to focus all his mind and energy to create life to comfort him. The first attempt he makes is a rose. He spends his days in meditation, ridding his thoughts of all but a rose. Miraculously, he finds a blooming rose along the oceanic coast and brings it inside, where it lives far longer than it should. Only when he begins to focus his thoughts on another object does it wither. Only it does not leave behind a dried and withered rose, but a repulsive piece of seaweed.
The narrator's next goal is loftier: the perfect woman. She will be his Companion, and as she is a product of his imagination, the woman of his dreams. Once again the experiment is successful-but after seeing the beautiful woman, she opens her mouth to reveal a set of vampire teeth. She is not a human woman, but a woman created from the sea. The narrator's dog jumps on her and kills her, leaving not a woman's corpse, but a "bloated, swollen obscenity of a thing long-drowned and dead, risen from slime and to that slime returning." A storm is upon the lighthouse, so fierce the narrator knows he won't survive. He secures his journal entries in a bottle around his dog's neck and waits to die, perhaps to join his Companion in the depths.
Note: Poe only wrote the first three days' worth of journal entries for this story, so no one knows what ideas he had for the story. Basically, the premise of the story was Poe's and all that follows was Robert Bloch. I don't know if he was aware of the connections to the fairy tale, and it's not a well known story so I haven't heard of fairy tale enthusiasts referring to it as a version of Beauty and the Beast, but the isolated man-magical rose-arrival of woman could easily pass for a slightly twisted and morbid version of the fairy tale.